The only difference I can think of is that with the pantyhose technique, the water flow per area of CYA exposed to it is VERY high -- perhaps around 15 GPM or so. In the filter, there is a lot of area so the CYA probably spreads out a bit and the flow rate is much slower since the 45 GPM or so total flow is spread out over the entire filter area.

I'm really just guessing, but PatL and followers of that technique swear by it as dissolving very quickly (i.e. 24 hours) while the skimmer to filter technique is know to still take many days to fully dissolve.

If the CYA was kept fully in the skimmer until it completely dissolved, then the probably 15 GPM flow rate through the skimmer would be equivalent to the return. However, unless you use a material to hold the CYA that has roughly the same filtering size as the filter, then whatever gets through that is bigger will end up stuck in the filter and subject to the lower flow rate.

Richard